A Superconducting IC Technology Based on Refractory Josephson Tunnel Junctions

E. L. Wolf

This chapter concerns the underlying refractory Josephson junctions that have dominated the voltage standard field since perhaps 1990. Before going into the issues in the technical development of refractory tunnel junctions, the chapter describes that a large effort was made at the IBM Corporation to develop a computer technology using Josephson junctions based on Pb alloys, including Bi and Au. The chapter focuses on the tunnel junction technology needed for the refractory metals, of which the most important is Nb, having the highest transition temperature, 9.26 K, among the elements. Fabrication of non-hysteretic shunted Josephson junctions is of interest to exploit the rapid single flux quantum (RSFQ) computing circuitry as a successor to the latching circuitry investigated earlier at IBM. A general feature of the Josephson arrays is design such that the linear array of junctions also serves as a stripline for the microwave propagation to the junctions.

S. Pagano, Sandro Barbanera, Vincenzo Boffa +6 more

Shuichi Tahara, Hideaki Numata, Shinichi Yorozu +2 more

V. Gubankov, K. Y. Constantinian, V. P. Koshelets +2 more

The electrophysics and microwave properties of Niobium oxide-barrier tunnel junctions with critical current densities up to 105A/cm2were studied. Millimeter wave mixing using strong nonlinearity of quasi-particle tunnelling curve is described. Nonhysteretic Josephson junctions obtained by the low inductance resistive shunting of the tunnel structures were investigated in the large frequency band. The frequency range where these junctions obey the resistively shunted junction model was determined. The shunted tunnel junctions have been shown to be suitable for various applications which require stable enough Josephson junctions with nonhysteretic I-V curve (IVC).

Tetsuo Yama

Michael Gurvitch, M. A. Washington, Harold A. Huggins

Preparation of high quality all-refractory Josephson tunnel junctions based on Nb/Al-oxide-Nb and Nb/Al-oxide-Al/Nb structures is reported. Critical currents up to 1300 A/cm2 and Vm values up to 35 mV were obtained. The specific capacitance of these junctions is 0.06±0.02 pF/μm2. Junctions were fabricated using standard photolithography and a new plasma etching process coupled with anodization of Nb.